Chromogenic dees which are colorless or substantially colorless but form colors by the action of developers have heretofore been extensively used in various color forming recording materials such as pressure-sensitive copying papers, heat-sensitive recording papers and the like.
With the progress of recent development of electronics, the application of the chromogenic dyes has been increasingly enlarged in the field of information on the premises or the distribution of commodities, for example, P.O.P. (Point-of-Purchase) or P.O.S. (Point-of-Sale), where bar codes are prepared at the stage of users and the users read them by utilizing electromagnetic waves emitted from semiconductor lasers.
Under such circumstances, there is a pressing need for chromogenic dyes which absorb not only electromagnetic waves in the visible light regions but also electromagnetic waves in the near-infrared ray regions emitted from the semiconductor lasers at the time of forming colors.
There have been proposed the chromogenic dyes including, for example, phthalide type compounds as disclosed in Japanese Patent LOP Publn. Nos. 121035/1976, 121037/1976, 121038/1976, 115448/1980, 115449/1980, 115450/1980, 115451/1980, 115452/1980, 115456/1980, 167979/1982, 157779/1983, 8364/1985 and 27589/1985, thiofluoran type compounds as disclosed in Japanese Patent LOP Publn. No. 148695/1984, fluorene type compounds as disclosed in Japanese Patent LOP Publn. Nos.1199757/1984 and 226871/1985, and leucocyanine type compounds as disclosed in Japanese Patent LOP Publn. No. 230890/1985.
These compounds mentioned above, however, were not found to be sufficiently satisfactory with respect to light fastness of colors formed by the action of the developers and to percent absorption of electromagnetic waves in the near-infrared regions.